Conventional multiplexing techniques, such as for example, TDM (time-division multiplexing) make inefficient use of bandwidth in communication networks for certain applications (such as "bursty" input streams) because assigned time or frequency slots often go unused. Statistical multiplexing can be used to overcome these inefficiencies.
In statistical multiplexing, a communication link is multiplexed between channels on a probabilistic basis. With a large number of bursty connections, all of the connections may be assigned to the same link with a high probability that they will not all burst information at the same time. If they do burst simultaneously, the burst can be placed in a physical buffer until a free time slot becomes available. Statistical multiplexing allows the sum of the peak bandwidth requirement of all connections to a link to exceed the aggregate available bandwidth of the link under certain conditions. Statistical multiplexing schemes generally provide for smaller average delays on a per-packet basis than TDM or FDM (frequency-division multiplexing). Statistical multiplexing is a distinguishing feature of ATM (asynchronous transfer mode) networks. Through the use of statistical multiplexing, significantly more users can be serviced than without statistical multiplexing, thereby increasing profits of the system or network operator.
Classic wire-based communication networks have long taken advantage of statistical multiplexing to increase network capacity in terms of the number of system users who are able to access the system simultaneously. FIG. 1 illustrates a prior art statistical multiplexer in a classic application. Several communication sources 100, 1-n in the example in FIG. 1, are connected to multiplexer 110 by separate lines or wires 120. Each line 120 has a capacity C.sub.i, where C.sub.i is greater than or equal to the full capacity of the source 100 it connects to multiplexer 110. The transmission capability of outgoing line 130 from multiplexer 110 has a capacity C.sub.out &lt;C.sub.T where C.sub.T is equal to the sum of all incoming transmission lines. If each source 100 transmits information or data continuously to another network node, such as network node 140, much of the information from one or more of the sources will be lost because the outgoing capacity is less than the total incoming capacity. However, if each or at least most, of sources 100 are statistical in nature, that is arrival of information from the source is bursty in nature, the statistical multiplexer will be able route nearly all of the incoming information to outgoing transmission line 130.
As information arrives randomly from each of sources 100, it is placed in a buffer 150. Processor 160 executes one or more multiplexing ("MUX") algorithms. Multiplexer 110 has one buffer 150 for each of input lines 120. Multiplexer 110 monitors the status of each buffer 150, transferring data from the buffer with the greatest occupancy to outgoing transmission line 130 for transmission to node 140. As a first buffer empties, a next buffer is switched to transfer data to outgoing line 130. In this manner the statistical multiplexer allows outgoing transmission line 130 to have less capacity than the sum of the capacity of all incoming transmission lines 120. This can represent a significant gain in efficiency for a communication system.
To date, the benefits of statistical multiplexing discussed above with respect to wire-based networks have not been fully realized in wireless networks taking advantage of the wireless interface. Multiplexing is generally done by establishing one-to-one links between the nodes of the system and combining individual sources in a multiplexer at the receiver end of the node.
What is needed is a method and apparatus to provide efficiency gain in wireless communication systems similar to that achievable through statistical multiplexing in wire-based communication systems. What is further needed is a method and apparatus to allow for improved efficiency gain in a communication system where system users (sources) are geographically distributed. What is further needed is a method and apparatus to allow for varying levels of quality of service (QoS) in a communication system which employs statistical multiplexing.